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  1. #131
    kb3lms's Avatar
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    Little Help?

    Finally, I have obtained a (complete) copy of Glafkides "Photographic Chemistry." One of the things I was interested in was a subbing recipe for acetate. At this point most of us are using wet-media PET films for actual coatings but I have been interested in subbing acetate one, because I never got it to work and two, because I have a small pile of acetate. Note, this is cellulose diacetate, not triacetate, according to the manufacturer website.

    I am aware that many here say that Glafkide's book has errors and omissions. OK, so knowing that, a subbing recipe given in Glafkides book for acetate is not terribly different from many I have read in patents. Here it is:

    • Gelatin 1g
      Acetic Acid 2g
      Water 4ml
      Nitrocellulose 1g
      Acetone 60ml
      Methanol 32ml


    According to the book, page 468, the gelatin, acetic acid and water are allowed to soak for a few hours and then melted in a water bath. The nitrocellulose is then added. So far, so good. Here is the problem: On adding the acetone, a white insoluble rubbery substance forms immediately. I assume the white substance has something to do with the gelatin. Any ideas what this white substance is and how to avoid having it form?

    I've had this happen most of the time when making acetate subbing formulas, which is one of the reasons I gave up on it. The acetone used is sold as 100% Acetone fingernail polish remover and the ingredients are given as acetone and denatonium benzoate, which is a bitter substance used at very low concentration.

    Thanks for any help,
    Jason
    All this has happened before, and all this will happen again.

  2. #132
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    Jason;

    In the first place, that appears to be a formula for subbing cellulose nitrate base not cellulose acetate. Also, the concentration of the Acetic Acid is not specified. I assume it is glacial AA. Heating too long or too hot will denature the gelatin.

    Acetone should be free of ALL contaminants. It should be chemically 100% Acetone and not have any denaturants.

    If you can get a better formula and better acetone, you will be better off. That formula is close to the ones I have seen though. Gelatin, AA, some plastic and a solvent. I'll take a look at my formulas here, but no promises. Everything I have worked with was presubbed.

    PE

  3. #133
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    Hi PE,

    Sorry, yes it is glacial Acetic Acid. What does denaturing the gelatin mean?

    Pre-subbed is definitely the way to go. The wet-media Grafix PET is great stuff, no frilling and no stripping but a bit on the pricey side.

    Not too long ago I obtained a 400 foot roll of clear 35mm triacetate film leader. It was manufactured by Kodak and is also pre-subbed. I suppose it is really just uncoated film base. Maybe it didn't meet their quality specs for use in a coated product so they sold it as leader.

    I will still probably get some pure Acetone. I do wonder about the denaturant in the acetone I have, though.

    Glafkides gives a simpler formula on page 467 for nitrate subbing consisting of:

    Gelatin 1.2g
    Acetic Acid (glacial) 2g
    Water 5ml
    Methanol 92ml

    Glafkides doesn't give a specific formula for subbing triacetate.

    Anyway, thanks and Happy New Year!

    -- Jason
    All this has happened before, and all this will happen again.

  4. #134
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    Jason, that latter formula should work.

    Denaturing gelatin is the process by which the tangled strands of gelatin change shape and can no longer dissolve in any liquid. It is too ionic for organic solvents and too non-polar for water. It forms a gooey whitish mass. I've done it many times by accident.

    Sometimes, all you have to do is reheat the mess and when it gets hot enough (30C - 40C) it will redissolve.

    You might try that. And watch out for the nitrocellulose. That is nasty stuff.

    PE

  5. #135

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    Interesting conversation, indeed, and probably way out of my league. But . . . I've coated a number of 2mm glass plates now, 4x5 through 8x10 and subbed with a thin layer of Minwax Polyurethane (spayed on). I've tray processed these plates and have had no lifting whatsoever. If that is of any value.

    Prior to learning about the Minwax, I couldn't keep the emulsion on the plates beyond the developer tray.

  6. #136
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    In the GEH workshop, the students coat directly on glass and have no adhesion problems. They don't even need hardener.

    However, coating on film is different. Film repels water much more vigorously than glass does.

    PE

  7. #137
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    I wonder if Pictorico would work. It would probably coat well, but major issue would probably be curling since it's quite thin.

  8. #138
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    Pictorico is intended for digital printing. As such, it has a mordant on the surface which can react with many chemicals. My tests so far have given me heavy brown stains in the Dmin region of all coatings made on any form of digital print material (paper or film).

    PE

  9. #139
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    Thank you, PE.

  10. #140

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    So, I took a sheet of 124CSS-VC Copier Transparency Sheet to see if it would accept a thin layer of Minwax Polyurathane. And it did. With that I expect it would accept the emulsion that I've been using. The sheets "may" accept an emulsion without subbing. Not something I plan on testing. One problem I noticed though . . . these sheets are magnets for dust. Handling them created a potential within the sheet.
    Last edited by DannL.; 01-01-2014 at 11:33 PM. Click to view previous post history.



 

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